Thermal relay



Patented Sept. 17, 1929 UNITED STATES PATENT OFFICE' EDWARD M. CLAYTOR, OF FOREST HILLS BOROUGH, PENNSYLVANIA, ASSIGNOR TO WESTINGHOUSE ELECTRIC8E MANUFACTURING COMPANY, A CORPORATION OF PENNSYLVANIA THERMAL RELAY Application filed May 14, 1927. Serial No. 191,332.

My invention relates to magneticthermal relays and particularly to relays in which the use of electro-magnct coils may be dispensed with. i

An object of my invention is to provide a thermal relay of the magnetic type that shall have an inverse time clniracteristic of operation.

Another object of my invention is to provide a thermal relay oi the magnetic type thatshall function properly without the utilization of an electromagnet coil.

A further object of my invention is to provide a thermal relay that shall operate to control-an electric circuit when a thermal element of the relay has been heated to a temperature at which it becomes non-magnetic.

A still further object of my invention is to provide a thermal element for a relay that shall be rendered non-magnetic upon being heated by an electric current to a tempera ture of a predetermined value, the time re quired for heating to this temperature being an inverse function of the quantity of current traversing the element.

And a still further object of my invention is to provide an auxiliary thermal element for a relay having a magnetically reversible thermal element, that shall check the operation of the relay at the higher values of currentand that. shall accelerate the operation at the lower values.

In the preferred form of my invention, a magnet, a magnetically reversible armature and a means for heating the armature are provided. In order to modify the eflect of the magnet upon the armature, an auxilairy thermal element is provided, the auxiliary element being responsive to the heating efi ect oi the heating means. In some applications,

the heating means and the armature may consist of an integral single piece.

For a fuller understanding of my invention, reference should be had. to the following description taken in conjunction with the accompanying drawings, in which,

Figure 1 is a view in side elevation of the relay embodying my invention.

1 Fig. 2 is a view in front elevation of the device illustrated in Fig. 1.

Fig. 3 is a top plan view of the same device, and

Fig. 4 illustrates the inverse time characteristic of my relay with reference to current and time.

. In the drawings, a base 10 is illustrated to which a pair of relatively stationary contacts 11 and 12 may be secured. As shown, portions of the contacts 11 and 12 extend to the right of the base 10, and other portions thereof project through the base, the latter portions being provided with cooperating nuts 13, with which they have screw-thread engagement in order that the contacts 11 and 12 may be secured firmly to the base.

Directly beneath the stationary contacts, a bracket 14 of substantially U shape is located, the bracket being secured to the base by bolts 15.

Between the outer ends of the bracket 14, a member l6, preferably of electric-insulating material, is disposed. The bracket may be pivotally secured thereto by means of a pin 17 that extends through alined openings in the member 16. and the bracket 14. The pin 17 may be provided with cotter pins 18 in order to prevent it from sliding out of its place. To a portion of the bracket or the member 16 extending below the pin17, a contact bridging member 21, of substantially T-shape, may be secured. the upper portion of the member 21 bridging the stationary contacts 11 and 12 as shown in Fig. 2 of the drawings.

The bridging member 21 may be secured to the member 16 by a bolt 22 that extends through an opening in the lower portion of the member 21, and a. corresponding opening in the lower portion of the member 16.

In order that the bridging member 21 may be yieldingly secured to the member 16. a spring 23 is provided, the spring being located between the right hand face of the member 16 and a washer 24 positioned at the outer end of the bolt 22. As shown, the washer 24 may be held in position against the compress'ion of the spring 23 by a cotter pin 25, the pin passing through the outer end of the bolt 22. p

.The upper end of the member 16 is provided with an arcuate shoulder, see Fig. 2, on which the bottom of a permanent horse-shoe magnet 26 may be supported. The horseshoe magnet 26 is located between the upper portion of the member 16 and aplate 28 of non-magnetic material.. The plate and the magnet may be firmly secured to the member 16 by a bolt 29 extending through the upper portion of the member 16 and the plate 28, and a knurled knob 31. As shown, the knob and the bolt have screw thread engagement with each other. As illustrated in Figs. 1' and 2 of drawings, the plate 28 is provided with an upwardly extending portion or lug 32 for a purpose to be hereinafter set'forth.

In order that a magnetic circuit may be COlIlpleted between the poles of the magnet 26, an armature 33 is provided that comprises a resistor element 34 and a magnetically reversible member The resistor 34, see Fig. 2, comprises a plurality of return bent convolutions, between the uppermost turns of which the member 35 may be placed.

In the particular embodiment of the armature 33 shown in the drawings, the magnetic member 35 comprises a strip of metal having portions cut away between the ends thereof in order that lugs 36 and??? may be provided. As shown, thealugs 36 and 37gai'e. bent over and against the top edfleo'ftheiuppermost turn of the resistor 34, th resistor being clamped between the lugs and the body portion of the member 35. The portion of the magnetic member that engages the poles of the magnet may be preferably of small section in order that magnetic flux concentration and a strong attraction may be effected between the member 35 and the poles of the magnet.

The reversible magnetic member 35 may be of a nickel iron alloy having the characteristic that when normally cool it will magneti-v cally cooperate with the magnet 26 to retain it in the position shown in the drawings, and when heated the alloywill cease to be magnetic at an appropriate temperature. A suitable material for this purpose comprises an alloy containing about one part of nickel to two parts of iron by weight. An alloy containing approximately 35% nickel and 65% of iron, with traces of other materials, is very suitable for efficient andreliable, operation of my improved relay. Such analloy ceases to be magnetic when heated to about 150 C. and becomes magnetic again when cooled to a slightly lower temperature according to the character of the alloy.-

Since the alloy is normally magnetic but becomes non magnetic when heated to a predetermined temperature, and upon cooling to a slightly lower temperature regains its magnetic characteristics, the alloy referred to above may be termed a reversible magnetic member, that is, it possesses reversible magnetic characteristics. Other nickel iron ale upper turn of'the loys having low transformation points are well known and may be embodied in the relay illustrated in the drawings, but the alloy referred to above is particularly useful in that the temperature at which the member 35 becomes non-magnetic is low and safe, but high enough so that the member 35 cannot be heated to the temperature at which it becomes non-magnetic by means other than the iiitended one.

Theresistor 34 issupportcd by a pair of terminals 38, the resistors being secured thereto by screws 39 that have screw thread engagement with the terminals 38. As shown, the terminals 38 project through open- I ings in the base 10 and are provided with to member 35 will then be heated in accordance with the current traversing the resistor.

lVhile the armature is illustrated as comprising a resistor 34 to which the mag netic member 35 is secured. it is to be understood that the armature 33 may be made of an integral strip, which strip may be an alloy of the type referred to above and hav ing the same characteristics. Such an armature is shown and described in my copending application, Serial No. 191,333, filed May 14, 1927, which is assigned to the Vestinghouse Electric & Manufacturing Company.

In order to modify the effect of the arinature 33 on the magnet 26, an auxiliary thermostatic element 41 is provided. As shown,

ing a slot 42 punched therein, the slot extending from the right hand end of the strip towards the central portion thereof. The right hand endof the bimetal strip therefore comprises strips 43 and 44. As shown, the end of the portion 43 is bent substantially in the shape of a V in order that this portion may latch or interlock with the lug 32 of the plate 28. The portion 44 is bent downwardly at substantially a right angle with the portion 43 and is located between the lugs of the magneticinember 35 that engages the poles of the magnet. The left hand end of the bii-nctal strip is bent at an angle in order that this portion may lie flatly against the base 10 so that it may be secured thereto by screws 40 or well known equivalents.

The portion 44 of the bimetal strip when heated pushes against the end of a screw 47 that has screw thread engagement with the plate 28. The screw may be adjusted in order that the initial pressure between the screw the element 41 comprises a bimetal strip liavlay. The screw 47 may be locked in the desired position by a lock nut 48.

Since the thermostatic member 41 receives its thermal energy from the resistor 34, its temperature will lag behind that of the resistor. The lag is particularly pronounced when the resistor is heated by a sudden rush of current, which current may be six or seven times the full load rating of an electric motor to be protected by the relay. In this event, the magnetic member 35'will be heated to the temperature at which it becomes non-magnetic before the latching strip 43 will have been released from the lug 32. As the temperature of the latch releasing strip 44 increases, the portion 44 will have deflected to such an extent that it will have pushed or forced the magnet 26 free of the latching strip 43. \Vhen the latching strip 43 has i. sen released from the lug 32, the member 16 and the magnet 26 carried thereby, will be caused to turn on the pin 17 which turning movement eilects disengagement of the contact bridging member 21 from the stationary con tacts 11 and 12. I

It is evident from Fig. 1 of the drawings that since the magnet 26 is located to one side of the pin 17, the tendency of the member 15 is to turn on the pivot17 in a clockwise direction, it being normally restrained from turning by means of the armature 35 and the latching strip 43. The relative movement between the magnet 26 and the magnetic member 35 is therefore eflected by the force of gravity. An additional force may be added by increasing the compression of the spring 23 when the magnet 26 is in the position shown in the drawings.

If a current of a smaller value traverses the resistor 34, for example, a current of twice normal value, the thermostatic member 41 will be heated to a temperature at which the strip portion 44 will effect a release of the magnet 26 from both the latching strip 43 and the magnetic member 35 before the latter has been heated to the temperature at which it becomes non-magnetic.

In Fig. 4 of the drawings, the inverse time characteristic of the relay illustrated in Figs. 1 and 3 is illustrated. As there shown, a curve 51 represents graphically the inverse time characteristic of the relay when the auxiliary thermostatic element 41 has been removed, the operation of the relay being effected only by means of the magnetic member 35. Curve 52, shown in broken lines, illustrates the inverse time characteristic of the relay when both the thermal characteristics of the thermostatic member 41 and the magnet member 35 are utilized.

In the event that the relay shown is oper ated in accordance with the curve 51, that is,

the auxiliary thermostatic element 41 beingremoved from the relay, a current represented by the ordinate to the line 53 will be required to flow through the resistor 34 for a. period of T seconds of time in order to heat the member 35 to the temperature at which it becomes non-magnetic. This current may represent a valve of substantially 600% normal current rating of the moton. to be protected, but in order that the reversibly magnetic member 35 may be heated to its non-magnetic ten'iperature in seconds of time, a relatively short period, the resistor 34 must be heated to an extremely high temperature which temperature may be injurious .to the resistor. At the lower values of current, the reversibly n'iagnetic member 35 is heated up quite slowly so that the time of tripping of the magnet 26 to ellect disengagement between the contacts 11 and 12 and bridging member 21, is longer than the desired time interval.

By modifying the eltect of the reversibly magnetic member 35 by means of the thermostatic latch 41, a larger resistor for a given value of current may be utilized, or with the same size resistor, a smaller value of current will be required to cause the relay to trip out in T seconds. The latch in this event retains the magnet 26 in the position shown in the drawings for a short interval after the member 35 has been so heated as to render it nonmagnetic.

As is evident from the curve, when a smaller value of current traverses the resistor 34, the heating of the thermostatic member 41 will follow more closely the heating of the armature 33, that is. the rate of heating of the armature is lower and the temperature difference between it and the thermostatic member is relatively small. WVhen this condition obtains, the strip 44 operates to disengage the magnet 26 from the magnetic member 35 and the latching strip 43 before the member 35 has been rendered non-magnetic. Generally stated, then, the effect of the thermostatic member 41 is to lower ordinates of the curve 51 to substantially the position Occupied by the curve 52 illustrated in broken lines. The characteristic of the curve 52 may be more desirable as it follows quite closely the heating and thermal characteristics of the apparatus to be protected. The shape of the lower portion of the curve 52 may be raised or lowered by means of the screw 47, that is, the pressure required on the screw 47 to release the magnet from the latching strip may be obtained at different temperatuies of the strip 41, depending upon the characteristic desired.

The relay illustrated in the drawings may be utilized, as previously stated herein, for protecting motors from being over-heated by excessive over-loads. In which cause it is to be understood that the terminals 38 may be connected in circuit with the motor to be protected and the contacts 11. and 12 may be connected in circuit with a switching mechanism for controlling the motor. When the contact bridging member 21 has been disengaged from the contacts 11 and 12, it is to be understood that the switching mechanism is so operated that the motor is tie-energized or disconnected from its supply lines.

Various modifications may be made in the device embodying my invention, without departing from the spirit and scope thereof. I. desire, therefore, that only such limitations shall be placed thereon as are imposed by the prior art and the appended claims.

1 claim as my invention:

1. An electromagnet device comprising a permanent magnet, an armature movable relatively to and normally engaging said magnot, said armature losing its magnetism at a temperature of a predetermined Value and regaining its magnetism upon cooling below the said temperature, means for passing an electric current through the armature to thereby effect heating thereof to its non-magnetiostate, a circuit interrupter, means for effecting relative movement between the magnet and the armature, means for utilizing the relative movement for actuating the circuit interrupter, and thermo-responsive means heated by said armature for checking the relative movement between the armature and the magnet when a sudden rush of current traverses the armature and for accelerating said movement when traversed by long continued lower values of current. I

2. An electromagnetic device comprising a permanent magnet, an armature movable relatively to and normally engaging said magnet, said armature losing its magnetism at a temperature of a predetermined value and regaining its magnetism upon cooling below the said temperature, means for passing an electric current through the armature where- .by the armature may be heated to its nonmagnetic state, a circuit interrupter, means for effecting relative movement between the magnet and the armature, means for utilizing the relative movement for actuating the circuit interrupter, a latch for holding said armature and magnet in engaged position for a predetermined length of time after the ar-' mature has been rendered non-magnetic in response to an abnormal current rush therethrough and thermostatic means for disengaging the armature from thelatch and the magnet before said armature becomes nonmagnetic when traversed by smaller values of current long continued.

3. An electromagnetic device comprising a permanent magnet, an armature movable relatively to and normally engaging said magnet, said armature losing its magnetism at a temperature of a predetermined value and regaining its magnetism upon cooling below the said temperature, means for passing an electric current through the armature Whereby the armature may be heated to its nonmagnetic state, a circuit interrupter, means for effecting relative movement between the magnet and the armature, means for utilizing the relative movement for actuating the circuit interrupter and thermostatic means comprising a latch and a latch releasing member, said latch being operable to hold the armature in one position for a predeter mined length of time when rendered nonmagnetic on a sudden overload and the latch releasing member being operable to release the latch and the armature before said armature becomes non-magnetic in response to smaller values of current traversing the armature for longer periods of time.

4. A circuit controlling device comprising a movable magnetic member, a circuit interrupter actuable thereby, thermostatic means for normally holding said movable member in a restrained position and for releasing the same when the thermal condition of said thermostatic means reaches a predetermined value, current traversed means for heating said thermostatic means, and means responsive to the temperature of the current traversed means for retarding the release of the magnetic member from said thermostatic means.

5. A circuit controlling device comprising a movable magnetic member, a circuit interrupter actnable thereby, thermostatic means for normally holding said movable member in a restrained position and for releasing the same when the thermal condition of said thermostatic means reaches a predetermined value, current traversed means for heating said thermostatic means and a magnetically reversible member for retarding the release of said movable member by said thermostatic means.

6. The combination with a protective device comprising a magnetically reversible member, a current traversed heating means therefor, a. gravity-actuated pivotally mounted permanent magnet normally engaging said reversible member while said member is magnetic and being disengaged therefrom when it becomes non-magnetic, of thermoresponsive means for retaining said permanent magnet in its normal position when said reversible member is rendered non-magnetic in response to sudden momentary rush of current through said heating means and for releasing said permanent magnet before the reversible member becomes non-magnetic when a current of a predetermined value has traversedsaid heating means for a predetermined length of time.

7. A protective device comprising a gravity actuated permanent magnet, a current-traversed magnetically reversible, member for normally restraining the permanent magnet against movement by theforce of gravity, and thermal means for retaining said permanent magnet in its normal position for a predeter:

mined length of time after said reversible member has been rendered non-magnetic in response to the heating effect of a current of several times normal value.

8. A protective device comprising a current-traversed magnetically-reversible memher, a pivotally-mounted gravity-actuated permanent magnet normally engaging said reversible member, and thermal means for actuating the permanent magnet out of engagement with said reversible member in advance of the temperature at which said reversible member becomes non-magnetic when predetermined values of current long continued traverse said reversible member, and for retaining said permanent magnet in engagement with said reversible member for a predetern'lined length of time after it has been rendered non-magnetic by an abnormal rush of current therethrough.

9. A circuit protector comprising a magnetic member actuable from one position to another, a circuit controlling member controlled thereby, a current-traversed magnetically reversible member for normally engaging said magnetic member and for releasing the salne from the reversible member when the reversible member has been rendered nonmagnetic by the heating elfect of a current of a predetermined value traversing said reversible member, of thermal means for delaying the release ofsaid magnetic member when a sudden abnormal value of current traverses said reversible member and for accelerating the release of said member when currents of smaller values have traversed the reversible member for predetermined lengths of time.

10. An electromagnetic device comprising a permanent magnet, an armature therefor, said armature being of a material that changes its permeability with the temperature thereof, and means for passing an electric current through said armature whereby the same is heated in response to the rate of current-flow, said armature having a reduced section adjacent to a point of contact with said magnet whereby a relatively hot spot is produced near said contact point by the current flowing through the armature.

11. In a circuit breaker, the combination with relatively movable contact members, of

a single thermally-actuable member embodying a latch portion and a portion effecting movement of one of said contact members.

12. In a circuit breaker, the combination with a fixed and movable contact member, of a bimetal member embodying a portion constituting a latch for said movable contact member and another portion operative to effect movement of said movable contact member.

In testimony whereof, I have hereunto subscribed my name this 7th day of May, 1927.

EDWARD M. CLAYTOR. 

